Most likely if you've modified your HTML code for the subscription form, then you've probably:

a)  removed some required hidden fields

b)  changed the form action path, or 

c)  broken the Javascript.

The best way to find out what went wrong is to get the HTML code of the subscription form from Pinpointe, test and make sure that its working, and then compare what you've changed to what was originally there. 

Pay special attention to the hidden form variables, the form tag itself and the Javascript verification code.